This project develops a theory of why humans and most other living beings senesce, in the sense of experiencing rising mortality and declining functional abilities as they grow older. Existing theories stress either the declining force of selection at older ages, as remaining net fertility declines (the classic or Hamilton theory), or tradeoffs between growth and reproduction when young and higher mortality when old (antagonistic pleiotropy or disposable soma). Both approaches ignore the role of intergenerational transfers (from parents or others to the young) in successful reproduction. The also ignore the closely related issue of the quantity-quality tradeoff between numbers of births and investment per birth. Drawing on extensive work in economic demography on intergenerational transfers and the quantity-quality tradeoff, this project develops a new formal theory of the evolution of aging, which includes the classic theory as a special case, and has new implications for the evolution of the life cycle of humans and many other species. The theory has broad implications in other areas, which will be developed for reproductive value, perturbations of the Leslie Matrix, inclusive fitness, and functionally heterogeneous social insects, among others. Empirical analyses will be pursued for a vadety of organisms including humans. Conceptual and calculational methods for estimating transfers will be developed.